Papermaking belts are well-known in the art. Papermaking belts are used to dewater and transport cellulosic fibers in a papermaking machine. The cellulosic fibers become an embryonic web and, upon drying, the finished product.
Typically, papermaking belts do not impart structure to the paper made thereon. "Structure" refers to variations in the basis weight and/or, more particularly, the density of the paper which are greater than occur in ordinary papermaking and due to ordinary variations, such as those induced by creping or wet micro-contraction. Such papermaking belts may be through air drying belts or conventional press felts. Such belts comprise a framework and a reinforcing structure through which water is removed.
Structured paper is consumer preferred because the paper can be softer, more absorbent, and utilize less fibers. However, producing structured paper typically has required through air drying, which can be costly.
The disadvantage to the aforementioned types of papermaking belts which are known to produce structured paper is that such papermaking belts are pervious to water. By being water pervious, the belts risk re-wet. Re-wet occurs when water removed from the paper being made on the belt is transferred away from the paper, then back to the paper. Re-wet occurs for many reasons. The typical cause of re-wet includes excess water carried by the felt to the point of introduction of the paper thereon.
Impermeable belts are also known in the art. For example, one impermeable belt has been commercially sold under the name Trans-belt by Albany International of Albany, N.Y. The Trans-belt, as well as other impermeable belts according to the prior art, suffer from the disadvantage that they do not produce structured paper when used as intended.
One attempt in the art to get around this disadvantage is to provide a patterned imprinting roll. The patterned imprinting roll is juxtaposed with the impermeable belt to form a nip therebetween. The paper travels through the nip between the belt and the patterned imprinting roll. In the nip, a pattern is imprinted on the paper yielding structured paper.
The structured paper then travels to a pressure roll where the paper is impressed in a second nip between the pressure roll and a Yankee drying drum. However, at the pressure roll, the structure previously imprinted into the paper is diminished or even lost, due to the compaction at this second nip. The compaction at this second nip between the pressure roll and the Yankee flattens the paper, causing the structure created at the nip between the trans-belt and the imprinting roll to be lost.
This invention provides a papermaking machine with an impermeable belt. Furthermore, this invention provides a belt for use in such a papermaking machine and which produces structured paper. This invention produces structured paper on an impermeable belt without diminishing the structure during steps incident to the manufacturing process.